1. Field of the Invention
The present invention relates to a sheet-like object feeding apparatus for feeding stacked sheet-like objects one by one at high speed.
2. Description of the Related Art
Typical sheet-like objects, to which the present invention is applied, are bank notes, data cards and printed matters. Hereinafter, this kind of sheet-like object is called simply "sheet." The sheet is subjected to various kinds of mechanical processing. The number of sheets to be processed has recently increased more and more, and the enhancement of processing performance in processing machines has been desired.
In the case of bank notes, there is a need to prepare batches of bank notes, each having a predetermined number of back notes. If this work is done by a person, that is inefficient; thus, the work is normally performed by automatic processing machines. Each batch of bank notes is bound by a belt.
There are known two methods of separating stacked sheets from one another, i.e. a "leafing" method and a "slipping" method. It was reported by NAKAMURA et al. that the slipping method is suitable for high-speed feeding ("TOSHIBA REVIEW", Vol. 37, No. 5, pp. 439-442).
Now referring to FIGS. 1 to 6, a description is given of sheet feeding apparatuses utilizing two conventional methods for feeding sheets one by one at high speed and with accuracy.
FIG. 1 is a perspective view showing first prior art of the sheet feeding apparatus. As is shown in FIG. 1, a sheet feeding apparatus 100 comprises mainly a feed rotor 101 for feeding a sheet by the slipping method, a motor 102, and an epicyclic gear mechanism 103 interposed between the motor 102 and the feed rotor 101. The epicyclic gear mechanism 103 receives a torque from the motor 102 and converts the torque to intermittent rotary movement (non-uniform rotary movement) and transmits the movement to the rotor 101. The epicyclic gear mechanism 103 comprises a solar gear 108 and two planetary gears 109a and 109b.
A pulley 104 is fixed to a shaft 102a of the motor 102. An endless belt 106 is passed between the pulley 104 and a fly-wheel 105. The fly-wheel 105 is rotatably supported on a center shaft 107.
Both end portions of the center shaft 107 are fixed to a chassis frame (not shown). The solar gear 108 is fixed to that part of the center shaft 107, which is near a first end portion of the center shaft 107, and accordingly the solar gear 108 is not rotatable. The two planetary gear 109a and 109b are arranged around the solar gear 108. The two planetary gears 109a and 109b revolve around the solar gear 108, while rotating about their axes. The number of teeth of each of the planetary gears 109a and 109b is just half the number of teeth of the solar gear 108.
The two planetary gears 109a and 109b are arranged around the solar gear 108 symmetrically in respect of the center shaft 107. First end portions of rotary shafts 110a and 110b are fixed to the planetary gears 109a and 109b. The rotary shafts 110a and 110b are parallel to the center shaft 107. Second end portions of the rotary shafts 110a and 110b penetrate the fly-wheel 105. Arms 111a and 111b are formed at the second end portions of the rotary shafts 110a and 110b. End portions of the arms 111a and 111b are bent at right angles in a substantially L-shape. Pins 112a and 112b extend from the bent end portions of the arms 111a and 111b along the rotary shafts 110a and 110b. The pins 112a and 112b are inserted into slots 113a and 113b formed in a crank arm 113.
The crank arm 113 has, at both end portions thereof, slots 113a and 113b extending in the longitudinal direction. A first end portion of a cylindrical member 114 is fixed to a center region of the crank arm 113. The longitudinal direction of the slots 113a and 113b coincides with that of the crank arm 113.
The longitudinal axis of the cylindrical member 114 coincides with that of the center shaft 107, and a second end portion of the center shaft 10 is inserted into the cylindrical member 114. The crank arm 113 is situated concentrically with the center shaft 107. A second end portion of the cylindrical member 114 is fixed to a center region of the rotor 101.
FIG. 2 is a perspective view showing second prior art of the sheet feeding apparatus. A sheet feeding apparatus 150, too, comprises mainly a rotor 101 for feeding sheets by the slipping method, a motor 102 for driving the feed rotor 101, and an epicyclic gear mechanism 103 for converting a uniform rotary movement of the motor 102 to intermittent rotary movement of the rotor 101.
The above-described structure of the sheet feeding apparatus 100 of the first prior art is similar to the sheet feeding apparatus 150 of the second prior art; however, the latter has the following different structural features. The feature of the structure of the sheet feeding apparatus 150 resides in the connection between the arms 111a and 111b and the crank arm 113. Specifically, in the sheet feeding apparatus 150, conrods 115a and 115b are interposed between the arms 111a and 111b and both end portions of the crank arm 113. The arm 111a and one end portion of the crank arm 113 are connected by means of pins 112a and 116a, and the arm 111b and the other end portion of the crank arm 113 are connected by means of pins 112b and 116b. The other structure is the same as that of the sheet feeding apparatus 100; thus, the common structural elements are denoted by like reference numerals, and detailed descriptions thereof are omitted.
The operation of the conventional sheet feeding apparatuses 100 and 150 will now be described, taking the sheet feeding apparatus 150 as an example. The fly-wheel 105 is rotated by the motor 102. Since the rotary shafts 110a and 110b having arms 111a and 111b are inserted into the fly-wheel 105, the rotary shafts 110a and 110b are rotated about the axis of the fly-wheel 105 in accordance with the rotation of the fly-wheel 105. The first end portions of the rotary shafts 110a and 110b are secured to the planetary gears 109a and 109b, and the planetary gears 109a and 109b are rotatable around the solar gear 108a with which the planetary gears 109a and 109b are meshed. Thus, the rotary shafts 110a and 110b are revolved about the axis of the fly-wheel 105 (hereinafter referred to simply as "revolution" as distinguished from "rotation") in the rotational direction of the fly-wheel 105, while being rotated about their own axes (hereinafter referred to simply as "rotation" as distinguished from "revolution"). The second end portions of these rotary shafts 110a and 110b are provided with the arms 111a and 11b for revolving the crank arm 113 and the pins 112a and 112b. Since the crank arm 113 is freely rotatable by the center shaft 107, the crank arm 113 and cylindrical member 114 rotate and also the rotor 101 fixed to the cylindrical member 114 rotates. Although the motor 102 and fly-wheel 105 are rotated at uniform speed, the rotor 101 is rotated at non-uniform speed. The non-uniform speed rotation of the rotor 101 is achieved by the mechanism including the arms 111a and 111b and crank arm 113 and the epicyclic gear mechanism 103.
FIGS. 3A to 3D are side views illustrating the operation of the epicyclic gear mechanism 103 of the sheet feeding apparatus 150, as viewed in the X-direction in FIG. 2. Dot-and-dash lines indicate the solar gear 108 and planetary gears 109a and 109b. Broken lines indicate how the meshed point between the solar gear 108 and planetary gear 109a moves from the state shown in FIG. 3A in accordance with the rotation of the planetary gear 109a.
At first, the fly-wheel 105 is rotated in the Y-direction from the state shown in FIG. 3A. On the other hand, the planetary gears 109a and 109b arranged around the solar gear 108 are simultaneously revolved and rotated by the rotary shafts 110a and 110b which are simultaneously revolved and rotated by the rotation of the fly-wheel 105. Thus, the relative position between the planetary gears 109a and 109b and the fly-wheel 105 is varied. As is shown in FIGS. 3B to 3D, the meshed point moves along a cycloid curve (broken line).
Since the meshed point between the planetary gears 109a and 109b moves along the cycloid curve, the angle between each con-rod 115a, 115b and the crank arm 113 varies successively. By the variation in angle, the amount of rotation of the crank arm 113 is rotated at non-uniform speed in relation to the uniform speed rotation of the fly-wheel 105, and intermittent rotational movement having short time stopping at FIGS. 3A and FIG. 3B are transmitted to the feed rotor 101.
FIGS. 4A to 4C are cross sectional views of the feed rotor 101, as viewed in the X-direction in FIG. 2, illustrating the sheet feeding operation of the feed rotor 101. A bottom portion of the feed rotor 101 is situated close to, or in contact with, the stacked sheets 130. From this state, the feed rotor 101 is rotated in the Z-direction.
A stationary block 117 is situated within the feed rotor 101. A vacuum chamber 118 is situated within the stationary block 117. The vacuum chamber 118 is kept in a vacuum state by means of a vacuum pump (not shown). The stationary block 117 and vacuum chamber 118 are fixed to the center shaft 107. Even when the feed roller 101 is rotated, the position of the stationary block 117 and vacuum chamber 118 remains unchanged. The vacuum chamber 118 has a suction portion 118a communicating with the outer wall of the feed rotor 101.
A plurality of suction holes 119a, 119b . . . are formed in the peripheral surface of the feed rotor 101 at regular intervals. The suction holes 119a, 119b . . . are sufficiently close to the stacked sheets 120. Although only one group of suction holes 119a, 119b . . . are shown in FIG. 4, other groups of suction holes 119a, 119b . . . are formed on both sides of said one group of holes along the center shaft 107.
Two rollers 120a and 120b are situated outside the feed rotor 101 on both sides of a line tangential to the bottom of the feed rotor 101. The rollers 120a and 102b are rotated in the directions of arrows by motors (not shown). In addition to the rollers 120a and 120b, two rollers (not shown ) are provided. A roller 122 is situated between the roller 120a and one of the two rollers not shown. A convey belt 121a is passed over the roller 120a, 122 and said one of the two rollers not shown. Another convey belt 121b is passed over the roller 120b and the other roller not shown. The convey belts 121a and 121b are superposed on each other at the roller 122. By virtue of the superposition of the convey belts 121a and 121b, one sheet 130 can be surely held.
Subsequently, the method of successively feeding the sheets 130 will now be described. The vacuum chamber 118 is kept in the vacuum position and the feed rotor 101 is rotated. By the rotation of the feed rotor 101, the suction hole 119a is brought into contact with the suction portion 118a of the vacuum chamber 118 (FIG. 4A). The first sheet 130a of the stacked sheets 130 situated near the bottom of the feed rotor 101 is sucked and conveyed in the rotational direction of the feed rotor 101. (A member 123 is provided to prevent two or more sheets being fed simultaneously.)
When the feed rotor 101 is further rotated, the subsequent suctions holes 119b, 119c . . . are brought to the position of the suction portion 118a, and the effect of sucking/conveying the sheet 130a is enhanced (FIG. 4B).
The feed rotor 101 is further rotated and all suction holes pass by the suction portion 118a of the vacuum chamber 118. At this time, the left end (in FIG. 4) of the sheet 130a is clamped between the convey belts 121a and 121b and is conveyed by these belts in the convey direction. In this manner, the sheets 130 are conveyed one by one.
Regarding the intermittent rotational movement of the feed rotor 101, the rotational speed is slowest in the state of FIG. 4A. The rotational speed increases in the order of the states shown in FIG. 4B and FIG. 4C, and decreases once again in the state of FIG. 4A.
FIG. 5 is a graph showing the relationship between the rotation amount .theta. of the fly-wheel 105 and the rotation amount .theta. of the feed rotor 101. The abscissa indicates .theta./.pi. (=H), or the input angle expressed by regarding the rotational angle of fly-wheel 105 as being dimensionless. The ordinate indicates .phi. (radian), or the output angle of the feed rotor 101 associated with the sheet feeding. From the graph, it is understood that the feed rotor 101 moves in an intermittent manner.
Curves b5 and c5 indicate the variations in speed and acceleration of the feed rotor 101 in relation to H. (Although the values of the curves vary greatly in accordance with the value of .theta., these values are divided by .theta. and the square of .theta. in the dimensionless manner.)
As is clear from curves b5 and c5, curves b5 and c5 are not symmetrical in respect of a boundary of H=0.5. In particular, regarding curve c5, the absolute values thereof differ greatly at extreme values (maximum acceleration and maximum deceleration) at two points in the vicinity of H=0 and H=1.
The reason why the absolute values of acceleration differ so greatly is that the sheet feeding apparatus 150 employs the pin coupling mechanism including the con-rods 115a and 115b. If the pin coupling mechanism is employed as in the sheet feeding apparatus 150 shown in FIG. 2, the cycloid curve produced by the epicyclic gear mechanism 103 is symmetrical in respect of H=0.5; however, the intermittent rotation speed and acceleration speed are not symmetrical, as shown in FIG. 5. In the case of the conventional sheet feeding apparatus 150 wherein the absolute values of acceleration differ greatly at the time of maximum acceleration and maximum deceleration, the deceleration peak increases particularly at the time of rotation of the feed rotor 101 and considerable noise and vibration occurs, which is not practically desirable.
By contrast, these problems are solved by the sheet feeding apparatus 100 shown in FIG. 1. The curves of intermittent rotational speed and acceleration produced by the epicyclic gear mechanism 103 are symmetrical in the vicinity of H=0.5, and the peaks of acceleration and deceleration coincide.
However, the sheet feeding apparatus 100 shown in FIG. 1 has the following drawback. In the sheet feeding apparatus 100, the rotational movement of the planetary gears 109a and 109b about the arms 111a and 111b produces rotational movement of the crank arm 113, but most of the rotational movement of the planetary gears 109a and 109b is converted to linear slide movement of the pins 112a and 112b along slits 113a and 113b. Consequently, when the pins 112a and 112b slide, a large frictional force due to load torque acts on the inner surfaces of the slits 113a and 113b, resulting in low transmission efficiency of force. Simultaneously, considerable noise and vibration occurs due to slide friction.
In connection with this, there are techniques of preventing as much as possible the slide friction between the pins 112a and 112b and the slits 113a and 113b, as shown in FIGS. 6A and 6B. FIG. 6A shows a technique wherein rotatable rollers 123a and 123b are attached to the pins 112a and 112b, and FIG. 6B shows a technique wherein sliding members 124a and 124b having outer shapes matching the shapes of the inner surfaces of the slits 113a and 113b are provided. Either technique, however, requires high precision of parts, increasing manufacture cost. In addition, the problem of slide friction cannot completely be solved. Thus, unless the technique of FIG. 2 using the pin coupling mechanism, wherein slide friction is little caused, is employed, the force transmission efficiency cannot be improved.
In either prior art technique described above, the epicyclic gear mechanism 103 is used as movement converting means for obtaining intermittent rotary movement. In the case of the mechanism using gears, however, the life of the apparatus cannot be increased remarkably owing to wear of the gear surfaces.
In designing the sheet feeding apparatus, it is required that the stop time of the feed rotor be as long as possible in the case where the time for a single rotation of the feed rotor is constant, thereby surely feeding sheets. However, if the epicyclic gear mechanism is used, as stated above, only the intermittent rotation curve corresponding to the cycloid curve is obtainable. It is impossible to freely design the rotational acceleration of the feed rotor and increase the stop time of the feed rotor.
As described above, in the conventional sheet feeding apparatus, when the pin coupling mechanism is employed, a difference arises between the absolute values of rotational acceleration, and noise and vibration occurs. On the other hand, when the linear slide movement is utilized, force transmission efficiency is lowered, and noise and vibration occurs owing to slide friction.
Each conventional sheet feeding apparatus described above adopts the epicyclic gear mechanism; thus, the intermittent rotational movement cannot be varied. Consequently, the stop time of the feed rotor cannot be increased as much as possible, and the sheet cannot surely be fed.
Furthermore, in actual cases, there are damaged sheets to be fed, and it is necessary to handle sheets of various conditions. For example, it is necessary to increase the stop time of the feed rotor, when damaged sheets are fed, compared to the case of feeding normal sheets, thereby to feed the damaged sheets carefully.